The invention relates to a tubular heat exchanger having controlled and improved heat transfer through the liquid film that is normally present within the tube adjacent the tube wall and including a turbulator on the interior of the tube in contact with the inner surface of the tube wall in which the turbulator comprises expanded metal adjacent to this wall surface with spacing projections of selected length and configuration, with the bridges and strands of expanded metal being angled with respect to the axis of the tube and the wall surface to direct preselected amounts of the flowing liquid toward the wall surface to improve the heat transfer by controlling skin effect of the liquid without excessive pressure drop in the liquid flowing through the tube.